Classical linear feedback control systems utilized for automatic engine speed hold control provide commands to change engine speed based on the difference between a commanded and sensed engine speed. Therefore, such systems do not command a change in current throttle position until an engine speed error has occurred.
Certain types of engines, such as a carburetted, rotary engines, operate over wide range of engine speeds and the relationship between engine shaft horse power and throttle position is very non-linear. For such an engine, a purely linear feedback control system does not provide ideal control, particularly for the purposes of providing engine speed hold control. Such a linear feedback control system yields and unacceptably slow response time to system disturbances. The response time of the linear feedback control system may be increased by increasing control gains; however, such increased gains may make the system less stable.